1. Field of the Invention
The present invention relates to a pivot mechanism of synchronous hinge device.
2. Description of the Related Art
Along with the development of electronic apparatuses, various hinge devices have been developed and applied to panel products. By means of the hinge device, an electronic product composed of two foldable parts can be relatively 360-degree folded back onto itself. The electronic product can be smoothly rotated to a 360-degree fully opened position or rotated to a 0-degree fully closed position or rotated to any angular position therebetween and kept partially opened. Many kinds of synchronous or asynchronous hinge mechanisms have been developed and applied to the electronic products. A conventional synchronous hinge device includes multiple gears engaged with each other to synchronously open/close the two foldable parts of the electronic apparatus.
In order to conveniently carry and use the foldable electronic apparatus such as a notebook, the electronic apparatus has become lighter and lighter, thinner and thinner and smaller and smaller. For synchronously operating the two shafts of the dual-shaft hinge of the electronic apparatus, a gear transmission mechanism is generally employed and applied to the dual-shaft hinge. In general, the end sections of the two shafts are provided with driving gears and a middle gear set is used to transmit the power. In the case that a traditional spur gear mechanism is used for transmitting the power, the gear thickness or tooth face length of the engaged spur teeth has better allowable miniaturization condition and the axial engagement position between the teeth provides less restriction. However, it is still necessary to keep a full gap between the engaged teeth for smoothening the operation. This will lead to greater error in transmission. This not only affects the stability of the synchronous transmission between the transmission gears, but also lowers the possibility of shortening of the distance between the axes of the two parallel shafts. As a result, the miniaturization of the volume and thickness of the dual-shaft hinge is greatly limited. This obviously is unbeneficial to the requirement of lightweight and thinning of the entire electronic apparatus.
Alternatively, in order to synchronously rotate the two shafts of the dual-shaft hinge, two opposite guide threaded rods are disposed on the rotary shafts. A slide member or a roller member is assembled between the two guide threaded rods as a synchronous transmission member. During the reciprocal displacement of the slide block between the guide threaded rods, the slide block moves along the spiral grooves of the guide threaded rods of the two rotary shafts to synchronously rotate the two rotary shafts. On one hand, the slide member or the roller member is engaged in the spiral grooves of the guide threaded rods to reciprocally move and on the other hand, the slide member or the roller member needs to have a move tolerance. Therefore, a gap may exist between the guide threaded rods and the slide block. In the synchronous mechanism, such gap often leads to shake and displacement of the rotary shafts. As a result, the rotary shafts can be hardly stably operated. When the electronic apparatus is folded open and used by any angle, the locating effect and the stability of use of the electronic apparatus may be affected. Moreover, the two opposite guide threaded rods necessitate longer operation travel. This is unbeneficial to the miniaturization of the dual-shaft torque hinge.
Patent No. WO2005/101963 discloses a dual-shaft mechanism employing multiple conical (or bevel) gears to transmit power for synchronously rotating the two rotary shafts. The application of the conical gears is advantageous in that the power can be more stably transmitted. However, as well known by those who are skilled in this field, in application of the conical gears for transmitting power, the conical gears must have a sufficiently long cone distance or face distance. In addition, the engaged gears must be right aligned with each other. Therefore, the assembly of the conical gears necessitates higher axial precision for providing good and smooth engagement and transmission effect. In the above dual-shaft hinge, in the case that the middle conical gears are disposed between the lateral sides of the parallel rotary shafts for transmitting the power, due to the cone distance or the face distance, it will be impossible to minimize the distance between the two rotary shafts. Reversely, in the case that the middle conical gears are changed to be disposed at the end sections of the two parallel rotary shafts, more space at the end sections of the two parallel rotary shafts will be occupied. As a result, the entire transmission mechanism or structure will have a larger volume to occupy more room. Especially, the transmission mechanism applied to the notebook or a mini-type electronic apparatus fails to meet the requirements of lightweight and thinning of the electronic apparatus. This is not what we expect.
According to the above, with respect to the transmission mechanism that simply employs spur gear set or slide member or roller member between the two parallel rotary shafts, it is more possible to reduce the use space. However, due to the gaps between the teeth and the slide member, the synchrony and stability of operation of the two parallel rotary shafts will be both ill affected. With respect to the transmission mechanism employing conical (bevel) gears as the transmission members, a better contact and transmission stability can be achieved. However, such transmission mechanism is disadvantageous in that the volume of the electronic apparatus will be increased and more room is occupied. All the above problems still need to be overcome.